Electric motor control system



Feb. 18, 1947. A. F. KENYON ml. 2,416,180

ELECTRIC MOTOR CONTROL SYSTEM Filed Sept. 7, 1944 Variable Vol tags 33 Source Insulatz'an ['1 37 i i V 52 Leg Excitation 501/766 WITNESSES: INVENTORS Alonzo ,FKez-zyon and lg lar'd 6 6001:... 5 .11- W W ATTOR Patented Feb. 18, 1947 ELECTRIC MOTOR CONTROL SYSTEM Alonzo F. Kenyon and Willard G. Cook, Wilkinsburg, Pa., assignors to Westinghouse Electric Corporation, East Pittsburgh, Pa., a corporation of Pennsylvania Application September 7, 1944, Serial No. 553,052

7 Claims.

Our invention relates generally to control systems, and it has reference inparticular to control systems for rolling mills.

Generally stated, it is an object of our invention to provide a control system for reversing rolling mills which is simple and inexpensive to manufacture and is easy to operate.

More specifically, it is an object of our invention to provide for controlling the speed of an edger roll motor in a universal rolling mill relative to the speed of the main roll motor so as to compensate for the effects of a reduction at the main rolls in the material being rolled, regardless of the direction of operation of the mill.

Another object of our invention is to provide for increasing the effective speed range of the edger motor in a reversing mill without increasing the relative inertia of the motor.

Yet another object of our invention is to provide for controlling the speed of the edger motor in a universal rolling mill by controlling the voltage applied thereto independently of the voltage applied to the main motor, and in accordance with the mill reduction and the ratio of main and edger roll diameters.

It is an important object of our invention to provide for controlling the speed of the edger motor relative to the speed of the main motor by means of armature voltage control, so that the edger roll motor may have the same speed range by field excitation control as does the main roll motor.

A further object of our invention is to provide for changing the speed of the edger roll motor so that it may operate at different speeds relative to the speed of the main roll motor when the mill is operating in opposite directions.

Still another object of our invention is to provide for changing the speed of the edger roll motor relative to the speed of the main roll motor in a universal rolling mill by automatically varying the field excitation of an auxiliary buck and boost generator in the armature circuit of the edger roll motor whenever the direction of operation of the mill is changed.

Other objects will in part be obvious, and will in part be explained hereinafter.

Many reversing metal rolling mills, such as slabbing, plate, and structural shape mills are of the so-called universal type, having a set of horizontal main rolls to work on the top and bottom surfaces of the piece being rolled and a set of vertical edger rolls to work on the edges of the piece. Reductions for each pass through the mill may run a high as 30 to 40 percent in the main rolls, but seldom exceed 2 to 3 percent in the edger rolls. For the purpose of description,

a negligible reduction.

the direction from the edger to the main rolls is designated the forward direction, regardless of the location of the pulpit. When operating in the forward direction so that the piece travels from the edger rolls to the main mill rolls, the edger roll delivery speed must be the same as the main mill roll entry peed. If the main mill roll is making a 40 percent reduction in the thickness of the piece being rolled, the edger roll speed will therefore be only percent of the main mill roll speed. However, when operating in the opposite direction so that the piece being rolled travels from the main rolls to the edger rolls, the two sets of rolls must operate at practically the same speed since the edger rolls make only It is usual practice to make the main roll motor have a speed range by field excitation control of 2:1 or more, and to utilize this available range for normal range of rolling speed. Then the auxiliary edger roll motor must operate over a wider range of speed corresponding to the maximum reduction, that is, if the main roll motor speed range is 2.521 and the maximum reducis to be 40 percent, the edger roll motor operating speed range will be In practice the diameter of the main and edger rolls may vary due to both wear and different sizes of rolls, so that the operating speed range of the edger motor must be still further increased to take care of the combinations of new large main rolls and worn small edger rolls, or of worn small main rolls and new large edger rolls.

Earlier practice has been to make the edger motor speed range by field excitation control sufficient to take care of the combined ratios of main roll field range, reduction, and ratio of roll diameter. In some cases the main motor speed range has had to be kept smaller than otherwise desirable because of the inability to build the edger roll motor of sufiiciently wide speed range. In any event, the edger roll motor had to be of Wide speed range, resulting in poor commutating performance, and usually also in the edger roll motor having a higher proportional inertia than the main roll motor, which prevents rapid acceleration and deceleration.

In accordance withour invention these disad vantages may be overcome by making use of an auxiliary series buck and boost generator in the armature circuit of the edger roll motor. The auxiliary generator is provided with a plurality of field windings one of which is energized in accordance with the amount of reduction at the main rolls. Control means are provided for ren= dering this field winding effective only in the forward direction when the piece being rolled is travelling from the edger to the main rolls. Another of the field windings may be energized inaccordance with the ratio between the main and edger roll diameters and is adjustable to compensate for changes in this ratio due to wear of the rolls as well as through the use of difierent size rolls.

For a more complete understanding of the nature and objects of our invention reference may be made to the following detailed description, which may be read in connection with the accompanying drawing in which the single figure is a diagrammatic view of a universal rolling mill embodying the invention in one of its forms.

Referring to the drawing the reference numeral Ill may denote generally a universal rolling mill of the reversing type having a'pair of relatively movable horizontal main rolls H for rolling material 8 to a predetermined thickness and which may be operatively connected to a main roll motor [2 having an armature l3 and associated field windings l4 and I5. Located adjacent and in' advanceof the main rolls H are a pair of relatively movable vertical edger rolls I! for controlling the width of the material 8, and which may be operatively connected to an edger motor l8 having an armature l9 and associated field windings 20 and 2|.

Operation of the main and edger roll motors l2 and I8 may be effected by connecting the armatures l3 and IS in a Ward Leonard or variable voltage system which may be represented by a masterreversing switch 22 and a suitable source 23 of variable voltage, for controlling the speed of the motors over the lower portion of their speed range. Additional control of the motors l2 and It! may be effected by connecting the field windings l and 2| to a suitable source of variable voltage represented by the conductors 25. The

voltage applied to the field windings l5 and 2| 7 from the conductors 25 may be controlled in any suitable manner, such as by means of rheostat-s 21 and 28 which may be operatively connected to provide for jointly varying the excitations of the main and edger motors. The auxiliary field windings l4 and 20 of the motors may be connected to a source of excitation, either of a constant potential or variable voltage, as desired.

In order to provide for operating the edger roll motor H3 at different speeds in the forward and reverse directions to compensate for the different effects of a reduction in draft at the main rolls' ll, means such as the auxiliary buck and boost generator 30 may be provided. The

generator 30 may be driven by any suitable. substantially constant speed means, and may have an armature 3| connected in series circuit relation with the edger motor armature l9, and field windings 32 and33, which may be normally energized so as to cause the generator to reduce the voltage across the armature l9. A draft compensation rheostat 34 may be provided for varying the excitation of the field winding 33 in accordance with the particular reduction in draft being made at the main rolls, since the relative speeds of the main and edger motors in the reverse direction are dependent on the reduction at the main rolls.

With a view to rendering the field winding 33 effective when the mill is operating in one direction and ineffective when the mill is operating in the oppositedirection, switch means 35 may be provided. The switch means'35 may be effective to connect the field winding 33 to the source when the mill is operating in the forward direction, that is, when the piece being rolled is moving from the edger to the main rolls, Operation of the switch means 35 may be effected in accordance with the operating position of the master control switch 22 which reversibly connects the armatures i3 and IQ of the main and edger motors to the source 23. In the present instance the switch means 35 may be represented as operatively connected to the master switch 22 by means of a bar 31 of insulating material, the switch means 35 will in practice most likely be a separate solenoid operated contactor operated under the control of the master reversing switch.

In order to provide for compensating for the effects on the relative speeds of the main and edger motors of different sizes of main and edger rolls, as well as for wear of a given set of rolls, the field winding 32 of the auxiliary generator 30 may be connected to the source 23 by means of a wear compensation and roll size rheostat 38 which may be adjusted to preselect the excitation of the field winding for given sizes of main and edger rolls, so that it is either cumulative or differential with respect to the field winding 33.

With a given set of main and edger rolls I l and H the rheostat 34 may be adjusted to a predetermined setting for a given reduction of the material to be rolled at the main rolls. When operating in the forward direction with the master switch 22 in the right-hand position the auxiliary switch 35 is closed. Accordingly, the field winding 330i the auxiliary generator is energized so that the armature voltage thereof increases, thus decreasing the voltage across the edger motor armature. The edger motor operates therefore at a relatively low speed which will be substantially proportional to the entry speed of the main so that the voltage of the auxiliary generator 33 will be reduced. Accordingly, the voltage across the edger roll motor armature increases and the edger roll motor operates at a higher speed which may be substantially equal to the main roll delivery speed. 7

From the above description and the accompanying drawing it will be apparent that we have provided in a simple and effective manner for compensating for the differences in main and edger roll speeds in universal reversing rolling mills. By using an auxiliary series generator in the manner described Weare able to reduce the field control range and overall size of the edger roll motor and still provide an extremely wide operating speed range with completely satisfactory operating characteristics. The relative in ertia of the edger motor may thus be kept at a minimum by keeping the size of the motor as small as possible so that rapid acceleration and deceleration of the motor may be readily affected. The commutation of the edger motor is improved .and the control for the motors is greatly simis intended that all of the matter contained in the above description and shown in the accompanying drawing shall be considered as illustrative and not in a limiting sense.

We claim as our invention:

1. An electrical control system for a reversing rolling mill having main rolls and edger rolls comprising, a main motor and an edger motor disposed to be energized from a source of electrical energy, reversing means for controlling the direction of operation of said motors, control means operable to vary the speed of both motors jointly, and means operable in accordance with the operating position of the reversing means for varying the speed of the edger motor-relative to the main motor.

2. In a control system for a reversible rolling mill, electric motors for driving the main and edger rolls of the reversible rolling mill, means operable to simultaneously vary the operating speeds of the motors in predetermined relation, reversing means'operable to reverse the direction of operation of both the main and edger motors, and means controlled by the reversing means operable to reduce the speed of the edger roll motor relative to the main roll motor in the forward direction.

3. In a control system for the electric motors driving the main and edger rolls in a reversible rolling mill and each having an armature and a field winding, means for producing variable control voltages for simultaneously varying the speeds of the motor by effecting variable excitation of the field windings, means for producing a variable voltage for effectin energization of the armatures, means including an auxiliary generator having a field winding and an armature disposed to be connected in series with the edger motor armature, means for reversing the polarity of the voltage disposed to be applied to the main and edger motor armatures, and control means responsive to operation of said means for varying the excitation of the auxiliary generator field winding.

4. A control system for use with main and edger motors in a reversible rolling mill which have armatures and field windings, meansior producing variable voltages for effecting the energization of the field windings to efiect variations in the speeds of the motors in predetermined relation, means for producing variable voltages for jointly'effecting energization of the armatures from a common source, an auxiliary generator having an armature disposed-to vary the energization of the edger motor armature separately and having a field winding, means for effecting variable excitation of the auxiliary goneratorfield winding to accommodate different reductions in draft of a material being rolle, control means for reversing energization of the motors for effecting reversal of the direction of operation of both of the motors, and means operable in response to operation of the control means for increasing the excitation of the auxiliary generator field winding when the control means is operable to effect operation of the motors in the forward direction.

5. For use with a universal rolling mill having spaced pairs of horizontal main'rolls and upright edging rolls for rolling material main and edger roll motors for driving the main and edger rolls, respectively, each provided with an armature and a field winding, means for varying the speeds of the motors of the field by jointly varying the energization windings, an auxiliary generator having an armature connected in series circuit relation with the edger motor armature for varying the energization of the edger motor armature relative to the main motor armature and a plurality of field windings, means to vary the energization of one of the generator windings to vary the relative speed of the motors, means to varythe excitation of another of the auxiliary generator field windings in accordance with the reduction of material, and means operable to change the direction of operation of the motors and render said another auxiliary generator field winding effective only when the motors are operating in the forward direction.

6. For use with a universal rolling mill havirig horizontal main and vertical edger rolls, main and edger motors for driving the main and edger rolls, respectively, each having an armature and an associated field winding, means for supplying a variable voltage to the armatures for varying the speeds of the motors jointly over a predetermined speed range, control means operable to reverse the polarity of said voltage, additional means for supplying a variable voltage to the field windings for varying the speeds of the motors jointly over an additional speed range, an auxiliary generator having an armature connected in series circuit relation with the edger motor armature for varying the speed of the edger motor relative to the main motor and a plurality of field windings, circuit means for energizing said windings in accordance .with the variable voltage applied to the armature of the main and edger roll motors, and means for deenergizing one of the auxiliary generator field windings when the main and edger motor armature voltage is reversed.

7. In a variable voltage control system for a reversible rolling mill having horizontal main rolls for effecting an appreciable reduction'in material being rolled and vertical edger rolls, main and edger motors for driving the main and edger rolls respectively, each having an armature and a field winding, means for applying variable voltages to the armatures and-field windings to vary the speeds of the motors Jointly, means operable to reverse the polarity of the voltage applied to the armatures for eifecting reversalof the main and edger motors, an auxiliary generator having a plurality of field windings and an armature connected in series circuit relation with the edger motor armature for bucking or boosting the variable voltage applied to the edger motor armature, circuit means for energizing one of the auxiliary generator field windings and varying the energization thereof to vary the relative speed of the motors in order to compensate for different ratios of roll diameters between the main edger rolls, additional circuit means for energizing the other of the auxiliary generator field windings and varying the energization in accordance with the reduction in thickness of the material, and means responsive to operation of the reversing means for rendering said other field winding ineffective.

ALONZO F. KENYON. WILLARD G. COOK.

REFERENCES CITED UNITED STATES PATENTS Number Name Date Iverson Dec. 8, 1936 

